Effect of interleukin-1 gene functional polymorphism on dorsolateral prefrontal cortex activity in schizophrenic patients.код для вставкиСкачать
American Journal of Medical Genetics Part B (Neuropsychiatric Genetics) 144B:1090 –1093 (2007) Brief Research Communication Effect of Interleukin-1b Gene Functional Polymorphism on Dorsolateral Prefrontal Cortex Activity in Schizophrenic Patients Sergi Papiol,1* Vicente Molina,2 Araceli Rosa,1,3 Javier Sanz,4 Tomás Palomo,4 and Lourdes Fañanás1 1 Departament de Biologia Animal, Unitat d’Antropologia, Facultat de Biologia, Universitat de Barcelona, Barcelona, Spain Department of Psychiatry, Hospital Clı´nico de Salamanca, Salamanca, Spain 3 Unitat de Biologia Evolutiva. Facultat de Cie`ncies de la Salut i de la Vida. Universitat Pompeu Fabra. Barcelona, Spain 4 Department of Psychiatry, Hospital Doce de Octubre, Edificio de Medicina Comunitaria, Madrid, Spain 2 Hypoactivity of the dorsolateral prefrontal cortex (DLPFC) during cognitive tasks is among the most consistent findings in schizophrenia. The biological factors contributing to this hypofrontality are only partially known. Previous reports have shown the influence of genes mapped to IL-1 cluster (i) in the risk to develop schizophrenia and (ii) on brain morphological abnormalities in these patients. Moreover, Interleukin-1b (IL-1b), encoded by IL-1B gene (IL-1 cluster, chromosome 2q13) has a key role in dopaminergic differentiation and dendrite growth in developing cortical neurons. The authors explored the role of a genetic functional polymorphism at IL-1B gene in relation to DLPFC activity. DLPFC (left and right) metabolic activity was measured in a sample of 19 DSM-IV diagnosed schizophrenic patients of Spanish origin using a procedure based on MRI/PET image fusion. During PET studies, subjects performed a contingent Continuous Performance Test aiming to activate DLPFC. Functional promoter polymorphism 511 C/T (rs16944) of IL-1B gene was genotyped in these patients. Those patients who were allele 2 (511 T) carriers showed a lower metabolic activity in the left DLPFC with respect to patients homozygous for allele 1 (511 C) (U ¼ 16, z ¼ 2.32, P ¼ 0.02). Our results suggest that hypofrontality reported in some schizophrenic patients might be explained, at least in part, by this functional polymorphism at IL-1B gene. Genetic variants with influence on brain functionality may account for the neurocognitive heterogeneity observed in schizophrenic patients. ß 2007 Wiley-Liss, Inc. Grant sponsor: Fundació ‘‘La Caixa’’; Grant numbers: 99-11100, 99-042-00; Grant sponsor: Instituto de Salud Carlos III-FIS; Grant number: 02/3095; Grant sponsor: Spanish Ministry of Health, Instituto de Salud Carlos III, Red de Enfermedades Mentales (REM-TAP Network); Grant number: RETIC RD06/ 0011; Grant sponsor: Generalitat de Catalunya, DURSI; Grant number: 2005SGR00608. *Correspondence to: Sergi Papiol, B.Sc., Departament de Biologia Animal, Unitat d’Antropologia, Facultat de Biologia, Universitat de Barcelona, Av. Diagonal 645, 08028 Barcelona, Spain. E-mail: firstname.lastname@example.org Received 17 August 2006; Accepted 6 March 2007 DOI 10.1002/ajmg.b.30542 ß 2007 Wiley-Liss, Inc. KEY WORDS: Interleukin-1; schizophrenia; dorsolateral prefrontal cortex; hypofrontality; PET Please cite this article as follows: Papiol S, Molina V, Rosa A, Sanz J, Palomo T, Fañanás L. 2007. Effect of Interleukin-1b Gene Functional Polymorphism on Dorsolateral Prefrontal Cortex Activity in Schizophrenic Patients. Am J Med Genet Part B 144B:1090– 1093. INTRODUCTION Hypoactivity of the dorsolateral prefrontal cortex (DLPFC) during cognitive tasks is among the most consistent findings in schizophrenic patients. Experiments based on executive or working memory challenges (Wisconsin Card-Sorting Test, verbal fluency, Tower of London or n-back task) typically demonstrate hypofrontality, a reduced activity of DLPFC in schizophrenic patients with respect to healthy subjects [Weinberger et al., 1988; Barch et al., 2001; Glahn et al., 2005; Snitz et al., 2005]. The neural, molecular, and genetic underpinnings of this dysfunction and other functional/morphological brain features are nowadays an active topic of research in schizophrenia. Several studies have shown the influence of BDNF, DISC1, or COMT genes, among others, on brain morphology in schizophrenia [Agartz et al., 2006; Ho et al., 2006; Ohnishi et al., 2006]. On the other hand, few studies have analyzed the effects of genetic variability of candidate genes on brain activity in schizophrenia. Among them, COMT gene is a paradigmatic example of how a single polymorphism can modulate DLPFC activity and cognitive performance [Egan et al., 2001; Rosa et al., 2004b]. Recent studies have revealed that genetic variants at IL-1B and IL-1RN genes (IL-1 cluster, chromosome 2q13) might confer risk to schizophrenia and bipolar disorder [Katila et al., 1999; Papiol et al., 2004; Rosa et al., 2004a]. The same genetic variants have been reported to contribute to structural brain abnormalities such as ventricular enlargement (IL-1RN) [Papiol et al., 2005] and frontal gray matter (GM) deficits (IL1B) [Meisenzahl et al., 2001] in schizophrenic patients. Interleukin-1b (IL-1b), encoded by IL-1B gene, is a cytokine involved in neurodevelopmental processes [Nawa et al., 2000] as well as in acute and chronic neurodegeneration [Allan et al., 2005]. Studies in vitro have shown that IL-1b has an important role in the induction of the dopaminergic phenotype in mesencephalic neuronal precursors [Potter et al., 1999; RodriguezPallares et al., 2005] and in the regulation of dendrite growth in developing cortical neurons [Gilmore et al., 2004]. Owing to the role of this cytokine during neurodevelopment, and taking into account the results commented above regard- Interleukin-1b Gene and Cortical Activity in Schizophrenia ing case–control and morphometric association studies, it could be suggested that subtle quantitative changes in IL-1b expression may have consequences in functionality of the adult brain. A possible factor modulating these kind of changes is a functional polymorphism in the promoter region (511 C/T) of IL-1B gene which regulates IL-1b expression, where allele 2 (511 T) promotes a higher expression of the gene with respect to allele 1 (511 C) [Chen et al., 2006]. Our aim has been to investigate the hypothetical relationship between this functional polymorphism at IL-1B gene and DLPFC activity in schizophrenic patients during an attentional task which challenges frontal function. Sample included 19 schizophrenic patients of Spanish origin (12 males); 9 out of them were first episodes (FE) (mean age 28.0 6.2 years; illness duration 3.6 2.8 years) and 10 were chronic patients (mean age 39.5 11.2 years; duration 10.1 9.0 years). FE patients were medication naı̈ve and all chronic patients had been treated with haloperidol for a period longer than 1 month prior to PET acquisition, as a part of a different protocol [see Molina et al., 2003]. Ethical approval was obtained from Spanish local research ethic committees. Given the potential effect of illness duration, age, and medication on gene expression, we compared genotype and brain activity between FE and chronic patients. Patients provided a complete written informed consent before inclusion in the study. All procedures were carried out according to the declaration of Helsinki. Image analysis: in order to determine the metabolic activity in the DLPF cortex we used a procedure based on MRI/PET image fusion. This methodology uses the anatomical information of the MRI to allow detailed measurement of regional metabolic activity in the PET image [Molina et al., 2003]. MRI Protocol: magnetic resonance imaging studies were acquired on a Philips Gyroscan 1.5T scanner using a T1weighted 3D gradient echo sequence with the following parameters: matrix size 256 256, pixel size 0.9 0.9 mm (FOV & 256 mm), flip angle 308, echo time 4.6 msec, slice thickness 1.5 mm. PET protocol: PET studies were obtained in a SIEMENS Exact 47 tomograph, 20 minutes after injecting 370 MBq of 18FDG, while subjects performed a contingent visual Continuous Performance Test. Matrix size was 256 256 61, and slices were 2.6 mm thick. Subjects were instructed to push a button if T immediately followed the letter L, as presented on a computer screen. The interstimulus interval was 1 sec. After the placement of an intravenous line for FDG administration, the subject began the task, which was divided into four blocks of 5 min each, with a 1-min rest between each two blocks. FDG was administered 1 min after initiating the task. Patients were not performing the test anymore after being placed in the PET camera. Tracer activity values were proportionally normalized to the global activity of each PET [Frackowiak et al., 1997] thus representing relative activity. Total metabolic activity for each region of interest (ROI) was divided by the ROI volume, thus providing a measurement independent of the amount of tissue sampled. Segmentation: To obtain metabolic measurements, we used a method for semi-automated segmentation of the brain based on the Talairach reference system, similar to that described in Andreasen et al. . Basically, we used a two-step procedure [Desco et al., 2001]. The first step involved editing the MRI to remove skull and extracranial tissue, registration of PET and MRI, and an initial segmentation of cerebral tissues into GM, white matter (WM), and cerebrospinal fluid (CSF). In a second stage, we applied the Talairach reference system [Talairach and Tournoux, 1988] to define ROIs and to obtain final metabolic activity data (See Fig. 1). A Talairach grid was built for each individual case. 1091 Fig. 1. Sagital view illustrating a Talairach grid built upon an edited MRI and fused with the GM segmentation of the PET scan. The Talairach grid cells describing the dorsolateral prefrontal region (DLPF) are highlighted. This ROI is defined as the cortex encompassed in Brodmann’s areas 8, 9, 10, and 46, according to the Talairach Atlas. The edited MRI (without extracranial tissue) was coregistered with the PET study using the AIR algorithm [Woods et al., 1993]. Fusion results were visually checked in all cases and the observed co-registration was always optimal. An initial segmentation of cerebral tissue was performed using an automated method, currently included as a standard processing tool in the statistical parametric mapping (SPM) program [Ashburner and Friston, 1997]. This method classifies all MRI pixels into four tissue types: GM, WM, CSF, and ‘‘other tissues:’’ This segmentation was checked for inconsistencies and manually corrected whenever necessary by an experienced radiologist blinded to the diagnosis. In the second stage, the ROI’s were obtained by superimposing the 3D tissue masks corresponding to WM, GM, and CSF onto each subject’s Talairach reference grid (Fig. 1), where the regions of interest were defined as sets of cells. On the PET/ MRI fused images, activity was measured by totaling the data from the grid cells associated with each ROI [Desco et al., 2001]. The DLPF cortex was defined as the cortex encompassing Brodmann’s areas 8, 9, 10, and 46 (Fig. 1). 511 C/T polymorphism (rs16944) located on the promoter region of IL-1B gene was genotyped as described by Katila et al. . Briefly, allele 1 (511 C) of IL-1B gene completes an AvaI restriction site, while allele 2 (511 T) gives an intact product. According to previous reports highlighting allele 2 as an allele of risk both for schizophrenia or its associated brain abnormalities [Meisenzahl et al., 2001; Rosa et al., 2004a], two subgroups of patients were generated: allele 2 carriers (allele 1/allele 2 and allele 2/allele 2) (n ¼ 11) and no-carriers (allele 1/allele 1) (n ¼ 8). There were no differences in sex distribution, treatment, or time from onset between both subgroups. FE and chronic patients did not significantly differ in terms of metabolic activity (left side FE 97.53 6.97, chronics 94.43 3.38, U ¼ 31, z ¼ 1.14, P ¼ 0.25; right side FE 102.66 7.85, chronics 100.19 3.39; U ¼ 32, z ¼ 1.06, P ¼ 0.31) neither on distribution of genotypes (FE five noncarriers, four carriers; chronics four noncarriers, seven carriers, w2 ¼ 1.81, P ¼ 0.37). We found a significantly lower metabolic activity in the left DLPFC in those patients with at least one allele 2 (mean 93.55 5.51) with respect to patients homozygous for allele 1 (mean 99.13 3.55) (U ¼ 16, z ¼ 2.32, P ¼ 0.02) (see Fig. 2). In the right DLPFC, differences were not significant (allele 2 carriers: mean 100.32 6.72; allele 1: mean 102.79 4.55; 1092 Papiol et al. particular biological traits, we are increasing our power to detect the effect of genetic variability on their expression within schizophrenic patients. Likewise, more research on IL-1 family of cytokines is warranted in order to (i) unequivocally establish their role both in neurodevelopment and in the adult brain and (ii) identify genetic variants with a repercussion on both gene expression and brain functionality. In conclusion, the present finding enhances the interest of neuroimaging-based techniques in ongoing and future genetic studies of schizophrenia in order to understand genetic and cognitive heterogeneity within this diagnostic group. ACKNOWLEDGMENTS Fig. 2. Values of metabolic activity during an attentional task for the left DLPFC according to IL-1B genotype. Patients who were allele 2 carriers of 511 C/T polymorphism of IL-1B gene show a significant decrease (P ¼ 0.02) in metabolic activity with respect to patients allele 1 homozygous. U ¼ 31, z ¼ 1.07, P ¼ 0.31). Although we did not include healthy controls in this genetic study, those metabolic ratios in patients are very similar to those found to be significantly lower than in healthy controls in a sample of FE of schizophrenia partially overlapping with the present one and using the same methodology [Molina et al., 2005]. Our results, although preliminary, suggest that 511 C/T functional polymorphism at IL-1B gene might contribute to explain hypofrontality reported in some schizophrenic patients. The present finding can be interpreted from a dopaminergic hypothesis perspective. The view that dopaminergic system plays a role in schizophrenia is long-standing [Carlsson, 1988]. Genetic studies focused on COMT, a key regulator of dopaminergic neurotransmission, have highlighted the outstanding influence of dopaminergic system on DLPFC activity, therefore, reinforcing this notion [Egan et al., 2001]. This dopaminergic background enhances the interest of in vitro studies showing that IL-1b is a key developmental factor inducing a marked increase in generation of dopaminergic-like neurons from neuronal precursors, maybe through induction of specific receptors responsive to additional factors [Ling et al., 1998; Potter et al., 1999; Rodriguez-Pallares et al., 2005]. It could be hypothesized that changes in IL-1b expression, maybe mediated by functional polymorphisms like 511 C/T, may lead to subtle differences in neurons relevant to dopaminergic system neurotransmission. The final repercussion of this fine abnormality would manifest as a differential pattern of DLPFC activity due to the fact that dopamine has an extreme functional importance in the attentional tasks in the frontal lobe [Fuster, 1999]. Further studies in larger samples would be necessary in order to rule out the possibility of a spurious association in our results because the limited sample size is certainly a remarkable limitation of the present study. However, it should be noted that the statistical error generated by a low-sample size could be minimized by the fact that according to our hypothesis, molecular underpinnings of brain functionality (in our case DLPFC activity) are influenced by a lower number of genes than the complex phenotype of a mental disorder defined by categorical diagnoses. Therefore, by analyzing these The authors would like to thank the participating patients and their families, whose generous contributions have made this study possible. This study was supported by grants from Fundació ‘‘La Caixa’’ (99-111-00), (99-042-00), FIS (02/3095) and by the Spanish Ministry of Health, Instituto de Salud Carlos III-RETIC RD06/0011, Red de Enfermedades Mentales (REM-TAP Network). Sergi Papiol was supported by a grant of the Ministry of Education and Culture of Spain. REFERENCES Agartz I, Sedvall GC, Terenius L, Kulle B, Frigessi A, Hall H, Jonsson EG. 2006. BDNF gene variants and brain morphology in schizophrenia. 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